Refactor the footer logic to a new file (#4259)

This will help us have more control over the footer

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Co-authored-by: pakrym-oai <pakrym@openai.com>

codex-rs/tui/src/bottom_pane/mod.rs

@@ -23,6 +23,7 @@ mod chat_composer_history;
 mod command_popup;
 pub mod custom_prompt_view;
 mod file_search_popup;
+mod footer;
 mod list_selection_view;
 pub(crate) use list_selection_view::SelectionViewParams;
 mod paste_burst;